The invention relates to a sheet detector for use in a sheet feed station of an equipment such as a facsimile system, and more particularly, to an apparatus which detects the presence or absence in the feed station of an "original" sheet for transmission which is used in a facsimile transceiver system or the like.
In an equipment utilizing a first and a second sheet, such as a record sheet for reception and an "original" sheet for transmission in a facsimile transceiver system, or a copy sheet and an "original" sheet (or a master plate in a printing machine) in a copying machine and an offset printing machine, it is necessary to change the function of the equipment depending on whether the first or the second sheet is being fed. Taking a facsimile transceiver, for example, when the first sheet or the record sheet for reception is being fed into an information recording section of the transceiver, the latter must be set in a receive mode while when the second sheet or an "original" sheet for transmission is fed into the transmitting section of the transceiver, the latter must be set in a transmit mode.
A switching of the equipment so that it is capable of functioning in a manner corresponding to the first or the second sheet being used is usually achieved by a manual operation by an operator as either sheet is used. In one example, there are provided a pair of cassettes which receive the first and the second sheet, respectively, and a procedure to set either the first or the second cassette in position on the sheet feed station is utilized to switch the function of the equipment. Alternatively, the equipment is normally maintained in a condition in which it has the function corresponding to the first cassette, but is switched to another function by a procedure of setting the second cassette in position. The first and second cassettes are disposed one above another in the sheet feed station of the equipment and are selectively brought into facing relationship with a sheet feed member, for example, a sheet feed roller, of the station by a manual operation of an operator. While the function of the equipment may be conveniently switched in dependence upon the intended cassette to be used, there is a disadvantage that the equipment is switched to the function corresponding to the second sheet whenever the second cassette is set in position , irrespective of whether the second cassette actually contains in available sheet therein.